<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<div id="div_id">我是一个div标签</div>
<script>
    // document.write("<h1>我是一级标题</h1>")
    var demo = document.getElementById("div_id")
    demo.innerHTML = "<h1>我是一级标题</h1>"
</script>

</body>
</html>